E-4 Buffers and Titrations

Question 1

Is the following solution a buffer?

HCl in H₂O

Answer 1

not a buffer - this is a strong acid and water

Question 2

Is the following solution a buffer?

NaOH in H₂O

Answer 2

not a buffer - this is a strong base and water

Question 3

Is the following solution a buffer?

HCl and NaOH in H₂O

Answer 3

not a buffer - this is a strong acid and a strong base - this will neutralize to form NaCl and water

Question 4

Is the following solution a buffer?

HNO₂ in H₂O

Answer 4

not a buffer - this is a weak acid and water

Question 5

Is the following solution a buffer?

NaNO₂ in H₂O

Answer 5

Not a buffer - this is a weak base and water

Question 6

Is the following solution a buffer?

HNO₂ and NaNO₂ in H₂O

Answer 6

This is a buffer - nitrous acid is a weak acid and the nitrite ion is its conjugate base

Question 7

Is the following solution a buffer?

HNO₂ and NaF in H₂O

Answer 7

Not a buffer - nitrous acid is a weak acid but the fluoride ion is not its conjugate base

Question 8

Is the following solution a buffer?

NaHSO₄ and H₂O

Answer 8

Not a buffer - This is a weak acid and water

Question 9

Is the following solution a buffer?

NaHSO₄ and Na₂SO₄ in H₂O

Answer 9

This is a buffer - the bisulfate ion is a weak acid the the sulfate ion is its conjugate base

Question 10

Is the following solution a buffer?

NH₃ in H₂O

Answer 10

Not a buffer - this is a weak base in water

Question 11

Is the following solution a buffer?

NH₄Cl in H₂O

Answer 11

Not a buffer - This is a weak acid in water

Question 12

Is the following solution a buffer?

NH₃ and NH₄Cl in H₂O

Answer 12

This is a buffer - ammonia is the weak base and the ammonium ion is its conjugate acid

Question 13

Which solution has the higher buffer capacity?

Current pH = 4

1. A 100 mL sample of buffer made from HNO₂/NaNO₂ when pK_a of HNO₂ is 3.40
2. A 100 mL sample of buffer made from HClO/NaClO when pKa of HClO is 7.5

Answer 13

Solution 1 - pKa of the acid is closest to the pH of the solution which will make the ratio of weak acid to conjugate base closer to 1:1

Question 14

Which solution has the higher buffer capacity?

1. A 100 mL sample of buffer made from from equal amounts of 1.0 M HNO₂ and 1.0 M NaNO₂
2. A 100 mL sample of buffer made from from equal amounts of 0.10 M HNO₂ and 0.10 M NaNO₂

Answer 14

Solution 1 - The higher total concentration has the best buffer capacity

Question 15

Which solution has the higher buffer capacity?

1. A buffer made from from 50mL of 1.0 M HNO₂ and 50 mL of 1.0 M NaNO₂
2. A buffer made from from 20 mL of 0.10 M HNO₂ and 80 mL of 1.0 M NaNO₂

Answer 15

Solution 1 - the buffer whose ration of weak acid to base is closer to 1:1 will have the higher buffer capacity

Question 16

Which curve represents a weak acid being titrated with a strong base?

Answer 16

This one

Question 17

Which curve represents a strong acid being titrated with a strong base?

Answer 17

This one

Question 18

Which curve represents a strong base being titrated with a strong acid?

Answer 18

This one

Question 19

Which curve represents a weak base being titrated with a strong acid?

Answer 19

This one

Question 20

Which point represents the equivalence point?

Answer 20

E

Question 21

Which point represents the 1/2 equivalence point?

Answer 21

C

Question 22

At this point a buffer exists where there is more weak acid than conjugate base.

Answer 22

B

Question 23

At this point a buffer exists where there is less weak acid than conjugate base

Answer 23

D

Question 24

At this point a buffer exists where the amount of weak acid is the same as the amount of conjugate base

Answer 24

C

Question 25

At this point a the weak acid has been neutralized and the amount of conjugate base determines the pH.

Answer 25

E

Question 26

At this point the weak acid has been neutralized and the amount of excess strong base determines the pH?

Answer 26

F

Question 27

At this (these) point(s) the [H₃O⁺] is greater than the [OH^-].

Answer 27

A, B, C, and D - the pH is less than 7

Question 28

At this (these) point(s) the [H₃O⁺] is less than the [OH^-]

Answer 28

E and F - the pH is greater than 7

Question 29

At this point no strong base has been added and the amount of weak acid determines the pH.

Answer 29

A

Question 30

Which of the following represents the equivalence point?

Answer 30

E

Question 31

Which of the following represents the 1/2 equivalence point?

Answer 31

C

Question 32

The weak base has been nuetralized and the excess strong acid determines the pH.

Answer 32

F

Question 33

At this point the no strong acid has been added and the amount of weak base determines the pH.

Answer 33

A

Question 34

The weak base has been neutralized and the amount of conjugate acid determines the pH.

Answer 34

E

Question 35

At this point a buffer exists where the concentration of the weak base and the conjugate acid are the same.

Answer 35

C

Question 36

At this point a buffer exists where the concentration of the weak base is greater than concentration of the conjugate acid.

Answer 36

B

Question 37

At this point a buffer exists where the concentration of the weak base is less than concentration of the conjugate acid.

Answer 37

D

Question 38

The [H₃O⁺] > [OH^-].

Answer 38

E and F - the pH is less than 7

Question 39

The [H₃O⁺] < [OH^-].

Answer 39

A, B, C, and D - the pH is greater than 7